U.S. patent number 4,521,912 [Application Number 06/502,679] was granted by the patent office on 1985-06-04 for low power indicating circuit for a radio transmitter.
This patent grant is currently assigned to General Electric Company. Invention is credited to Wayne J. Faulkenberry, Earnest A. Franke.
United States Patent |
4,521,912 |
Franke , et al. |
June 4, 1985 |
Low power indicating circuit for a radio transmitter
Abstract
Low power for a radio transmitter is indicated by an output
power detector voltage falling below a low power reference voltage
derived from an existing power control circuit.
Inventors: |
Franke; Earnest A. (Goode,
VA), Faulkenberry; Wayne J. (Lynchburg, VA) |
Assignee: |
General Electric Company
(Lynchburg, VA)
|
Family
ID: |
23998891 |
Appl.
No.: |
06/502,679 |
Filed: |
June 9, 1983 |
Current U.S.
Class: |
455/115.1;
455/126 |
Current CPC
Class: |
H03G
3/3042 (20130101); H04B 17/18 (20150115); H04B
17/102 (20150115) |
Current International
Class: |
H04B
17/00 (20060101); H03G 3/20 (20060101); H04B
017/00 (); H04B 001/02 () |
Field of
Search: |
;455/115-117,127,126
;330/27P,127 ;340/539 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ng; Jin F.
Attorney, Agent or Firm: Williams; J. J. Lampe, Jr.; R.
C.
Claims
What we claim as new and desire to secure by Letters Patent of the
United States is:
1. A low power indicating circuit for a radio transmitter
comprising:
a. an output power magnitude detector for coupling to the output of
said radio transmitter and producing a power magnitude signal
related thereto;
b. first means for providing a selectable power magnitude reference
signal;
c. second means coupled to said output power magnitude detector and
to said first means for producing a feedback signal for application
to said radio transmitter to control said output power magnitude as
a function of the selected power magnitude provided by said first
means;
d. a low power magnitude circuit coupled to said first means for
selecting a low power magnitude signal therefrom;
e. third means coupled to said output power magnitude detector and
to said low power magnitude circuit for producing a low power
signal in response to said power magnitude signal being less than
said low power magnitude signal;
f. and means coupled between said third means and said radio
transmitter for shutting off said radio transmitter in response to
said low power signal.
2. A low power indicating circuit for a radio transmitter
comprising:
a. an output power magnitude detector for coupling to the output of
said radio transmitter and producing a power magnitude signal
related thereto;
b. first means for providing a selectable power magnitude reference
signal;
c. second means coupled to said output power magnitude detector and
to said first means for producing a feedback signal for application
to said radio transmitter to control said output power magnitude as
a function of the selected power magnitude provided by said first
means;
d. a low power magnitude circuit coupled to said first means for
selecting a low power magnitude signal therefrom;
e. third means coupled to said output power magnitude detector and
to said low power magnitude circuit for producing a low power
signal in response to said power magnitude signal being less than
said low power magnitude signal;
f. and means coupled to said third means for providing an alarm in
response to said low power signal.
3. The indicating circuit of claim 2 wherein said low power
magnitude circuit comprises a voltage divider circuit that provides
a selected fraction of said reference signal.
4. The indicating circuit of claim 2 wherein said third means
comprise a differential amplifier having one input connected to
said output power magnitude detector and the other input connected
to said low power magnitude circuit.
5. The indicating circuit of claim 3 wherein said third means
comprise a differential amplifier having one input connected to
said output power magnitude detector and the other input connected
to said voltage divider circuit at the location which provides said
selected fraction of said reference signal.
Description
BACKGROUND OF THE INVENTION
Our invention relates to a low power indicating circuit, and
particularly to such a circuit for use with an existing power
control circuit for a radio transmitter or the like.
In radio communication services, and particularly in mobile radio
telephone services, it is desirable to know if the output power of
a radio transmitter has fallen below a minimum acceptable value.
Such a minimum acceptable value is essential, or at least
desirable, in order to provide acceptable or high quality radio
communication. Such a minimum acceptable value is also essential to
protect a radio transmitter whose radio frequency power output may
drop because of some circuit fault, such as thermal runaway of the
power amplifier device. In addition, it is desirable to provide an
indication when a radio transmitter output power has fallen below a
minimum acceptable value. In the case of mobile radio telephone
service, such an indication can be used to alert a user that his
communication is not or may not be reaching a remote location, or
can be used to automatically transfer the radio communication to
another radio transmitter. Upon such a transfer, the radio
transmitter whose output power has fallen can be taken out of
service and its fault or problem corrected.
Radio transmitters are frequently provided with an output power
control circuit which maintains the output power of a radio
transmitter or the like at a selected magnitude. Hence, it is
desirable to utilize as much of a power control circuit as possible
to provide a low power indication.
SUMMARY OF THE INVENTION
Briefly, and in accordance with our invention, we provide a low
power indicating circuit for use with an already existing output
power control circuit having an output power detector, a reference
circuit, and a feedback circuit coupled from the power detector and
reference circuit back to the output power circuit. In accordance
with our invention, we derive a first signal from the power
detector, and derive a second signal of selected low power
magnitude from the reference circuit. Means coupled to the derived
signals provide an indication when the power detector signal is
less than the selected low power signal. This indication is
provided when the output power is less than the selected low power
signal, and can be used in any way desired, such as an alarm to a
user, or an automatic transfer of communication to another
transmitter, or to some combination of uses.
BRIEF DESCRIPTION OF THE DRAWING
The subject matter which we regard as our invention is particularly
pointed out and distinctly claimed in the claims. The structure and
operation of our invention, as well as advantages, may be better
understood from the following description given in connection with
the accompanying drawing, in which:
The single FIGURE illustrates a preferred circuit diagram of a low
power indicating circuit in accordance with our invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Our low power indicating circuit is primarily intended to be used
with a radio transmitter 10 or the like which typically includes an
audio input circuit, an audio amplifier, and an exciter. The output
of this transmitter 10 is applied to a power amplifier 11 which
includes tubes or solid state devices to provide suitable
amplification of the exciter output, usually modulated, for
application over a transmission line 12 to an antenna 13. As known
to persons skilled in the radio art, the power amplifier 11 must or
should be adjusted to provide the desired RF output power to comply
with FCC regulations and also to prevent overloading or damage to
the amplifier devices, which are usually transistors. This is
achieved by a power magnitude detector 15 which derives, either
directly or by coupling, a small portion of the output power. The
coupling is indicated by the dashed line between the line 12 and
the input of the detector 15. As known in the art, the power
magnitude detector rectifies this small amount of output power to
provide a voltage V.sub.D whose magnitude is indicative of and
usually directly related to the amount of output power. This
voltage V.sub.D is supplied to an output line 16 which is connected
to the minus (-) input of a differential amplifier DA1. The
negative sign indicates that it is an inverting input. The output
signal will be an inverted version of the signal on that input. The
plus (+) input of the differential amplifier DA1 is provided with a
reference voltage V.sub.R. This reference voltage V.sub.R is
provided by the movable tap of a power magnitude reference circuit
comprised of three resistors R1, R2, R3 connected in series between
a positive source of voltage and ground.
The output of the differential amplifier DA1 is coupled to the
input of a control circuit 18, whose output is coupled in feedback
fashion to the power amplifier 11. The control circuit 18 produces
the appropriate signal or control function that adjusts the output
power of the amplifier 11 in accordance with the feedback voltage
supplied by the differential amplifier DA1.
The circuit as described thus far is known in the art, one example
of such a circuit being shown in U.S. Pat. No. 4,114,108 issued
Sept. 12, 1978. As known to persons skilled in the art, the control
circuit 18 may vary the input power applied to the power amplifier
11 to control the output of the amplifier 11, or may vary the
excitation applied to the amplifier 11 as a function of the output
of the differential amplifier DA1.
In the operation of the circuit as described thus far, the movable
tap on the resistor R2 is set at some point to provide a voltage
which, by previous experience, causes the amplifier 11 to produce
the desired output power. If the output power, as detected by the
detector 15, exceeds the desired level, the differential amplifier
DA1 produces a negative voltage which causes the control circuit 18
to reduce this power. Conversely, if the output power is below the
desired level, the differential amplifier DA1 produces a positive
voltage which causes the control circuit 18 to raise the output
power.
In some applications, it is desirable or essential that the output
power supplied by the amplifier 11 not be allowed to fall below a
selected magnitude. This is necessary to make sure that sufficient
transmitter output power is produced to provide the desired quality
of radio communications. In accordance with our invention, we
provide a low power indicating and control circuit which is shown
enclosed in dashed lines in the FIGURE. As will become apparent,
this indicating circuit provides the desired low power indication,
but is also easily adapted to be used with the prior art power
control circuit just described. Our low power indicating circuit
utilizes a differential amplifier DA2 whose minus (-) input is also
coupled to the output line 16 of the power magnitude detector 15.
The plus (+) input of the differential amplifier DA2 is supplied
with a low power voltage V.sub.L. This voltage V.sub.L is provided
at the junction of two resistors R4, R5 connected in series between
the tap on the resistor R2 and ground. As will be explained, the
relative magnitudes of the resistors R4, R5 determine the low power
at which an indication is provided. This indication is produced at
the output of the differential amplifier DA2 and may be used to
actuate an alarm 20 that alerts a user that his transmitter is
producing low power, and that actuates a shutdown or turn-off
circuit 21 which turns off the radio transmitter 10 and power
amplifier 11. In addition, the shutdown circuit 21 may, if desired,
provide automatic switching of a given communication to another
radio transmitter and power amplifier.
The magnitude of the resistors R4, R5 provide a voltage V.sub.L at
the plus terminal (+) of the differential amplifier DA2 that is
R5/(R4+R5) times the voltage V.sub.R provided by the power
magnitude reference circuit. This provides a constant fraction or
ratio of the reference voltage V.sub.R, regardless of where the
setting for the tap on the resistor R2 is made. And as will be
apparent to persons skilled in the art, if the detector voltage
V.sub.D falls below the low power voltage V.sub.L, the differential
amplifier DA2 produces a positive voltage that indicates that the
power is low, with appropriate alarms and operations being
effected. However, if the detector voltage V.sub.D exceeds the low
power magnitude voltage V.sub.L, then the output of the
differential amplifier DA2 is negative, and no alarm or indication
is given.
It will thus be seen that we have provided a new and improved low
power indicating circuit which provides assurance and control if
the power of a radio transmitter falls below a selected magnitude.
Our circuit is easily adapted for use with an existing power
magnitude control circuit. While we have shown only one embodiment,
persons skilled in the art will appreciate the modifications that
may be made. The power magnitude detector 15, the voltage
difference circuits DA1, DA2, the control circuit 18, the shutdown
circuit 21, and the alarm 20 may take many different forms.
Likewise, the low power voltage V.sub.L may be derived from a
movable tap connected to the series of resistors R4, R5. Therefore,
while our invention has been described with reference to a
particular embodiment, it is to be understood that modifications
may be made without departing from the spirit of the invention or
from the scope of the claims.
* * * * *